An ultrasonic diagnostic apparatus provides information necessary for diagnosis of a test subject by radiating an ultrasonic wave into an organic test subject such as a human being or animal, detecting an echo reflected inside the test subject, and displaying a tomogram or the like of tissue inside the living organism. At this time, the ultrasonic diagnostic apparatus uses an ultrasonic probe for ultrasonic wave transmission into the test subject and reception of a reflected echo from inside the test subject.
FIG. 1 shows an example of this kind of ultrasonic probe. In FIG. 1, ultrasonic probe 10 is composed of a plurality of piezoelectric elements 11 arrayed in one direction (the X direction) for transmitting and receiving ultrasonic waves to/from a test subject (not shown), acoustic matching layers 12 comprising one or more layers (in FIG. 1, two layers 12a and 12b) provided on the test-subject-side front surfaces (at the top in FIG. 1) of piezoelectric elements 11, propagating medium 13 provided on the test-subject-side surface of these acoustic matching layers 12, and rear-surface backing material 14 provided on the rear surface forming the opposite side of acoustic matching layers 12 with respect to piezoelectric elements 11. Electrodes (not shown) are arrayed on the front surfaces and rear surfaces of piezoelectric elements 11. Electrical signals are supplied to piezoelectric elements 11 via these electrodes and electrical terminals 15. In piezoelectric elements 11, a plurality of grooves are formed from the acoustic matching layer 12 side, being formed into a concave shape in the direction (Y direction) orthogonal to the array direction (X direction) (see Patent Document 1, for example).
Piezoelectric elements 11 are formed from a PZT or similar type of piezoelectric ceramic, a piezoelectric monocrystal, or the like, convert an applied voltage to an ultrasonic wave and transmit this into a test subject, and receive an echo reflected from inside the test subject and convert this to an electrical signal. In the example shown in FIG. 1, a plurality of piezoelectric elements 11 are arrayed in the X direction. Arraying a plurality of piezoelectric elements 11 in this way enables ultrasonic waves to be electronically scanned and deflected or converged, making so-called electronic scanning possible.
Acoustic matching layers 12 are provided to transmit and receive ultrasonic waves efficiently inside a test subject. More specifically, acoustic matching layers 12 have a role of bringing the acoustic impedance of piezoelectric elements 11 close to the acoustic impedance of a test subject in steps.
In the example shown in FIG. 1, piezoelectric elements 11 and acoustic matching layers 12 are formed into a concave shape on the test subject side, and therefore have a function of focusing an ultrasonic wave beam, but since adhesion to a test subject is inadequate due to the concave shape, the configuration is provided with propagating medium 13 that includes a role of eliminating this inadequacy. Propagating medium 13 is an optional element, being provided as necessary.
Rear-surface backing material 14 is bonded to piezoelectric elements 11 and supports them, and also has a role of attenuating unwanted ultrasonic waves. In this specification, the X direction in a drawing may also be referred to as “the (piezoelectric element) array direction”, the Y direction as “the (piezoelectric element) width direction”, and the Z direction as “the (piezoelectric element) thickness direction”.    Patent Document 1: National Publication of International Patent Application No. HEI 8-506227